1. Field
The present invention relates to a 3-dimensional (3D) data encoding and decoding, and more particularly, to a method and apparatus for encoding and/or decoding 3D volume data.
2. Description of the Related Art
Among methods expressing a 3D object, a method using a polygonal mesh model is widely used. Meanwhile, depth image-based representation (DIBR), which was adopted as a standard for MPEG-4 Animation Framework extension (AFX) in 2003, is a method of expressing a 3D object using a set of reference images consisting of real images or synthetic images, instead of the polygonal mesh model. A reference image consists of images seen at surfaces of a hexahedron surrounding a 3D object as shown in FIG. 1. Each reference image includes corresponding color images and depth images. The color images represent colors of respective points on the surface of a 3D object, and the depth images represent distance values to respective points on the surface of the 3D object from corresponding surfaces of the hexahedron. In FIG. 1, total 12 reference images including 6 depth images and 6 color images seen at respective surfaces are shown.
Advantages of the DIBR method lie in that it does not need to use the complicated polygonal mesh model, and a 3D object can be visualized with a high picture quality because it uses images. There are three formats for the DIBR: SimpleTexture, PointTexture, and OctreeImage formats. Among them, PointTexture format expresses a 3D object by arranging all points sampling the 3D object into each scan line on one plane as shown in FIG. 2. Each point of the PointTexture is expressed by a color and a depth. The depth is a distance from the plane to the point. Additionally, the other attributes of the point can be included.
As shown in FIG. 2, since points constituting the surface of a 3D object can be arranged along each depth line of a plane onto which the points have been projected, the PointTexture format is generally formed of a plurality of layers. According to this, the PointTexture format has an advantage that it can express a complicated 3D object formed with multiple faces. However, when a dimensional object should be expressed realistically at a high sampling density, the amount of data becomes huge and a method capable of compressing the data efficiently is needed. In addition, a method for compressing PointTexture format data is needed.
The conventional compression method needs optimization for the amount of information to be transmitted and still the amount can be reduced. When the compressed bitstream is restored, a method for more natural visualization is needed.
In a MPEG meeting held in July, 2003, an octree compression method using a prediction by partial matching method has been suggested for PointTexture compression in the MPEG-4 AFX standard. However, this method cannot smoothly visualize images when reading progressive bitstreams and restoring images. Also, since this method uses the octree compression method, there is a drawback that in relation to the resolution of volume data, only data with a fixed resolution in which the values of the width, height, and depth should be identical can be compressed. That is, data having an arbitrary resolution in which the values of the width, height, and depth are different to each other cannot be compressed.
Accordingly, a method capable of progressive transmission and more natural visualization in restoration, as well as effective compression of 3D object data having an arbitrary resolution is needed.